The present invention relates to an electronic device for starting a synchronous motor with permanent-magnet rotor particularly suitable, in its configuration, for starting a motor with two stator poles and two rotor poles.
As is known, synchronous motors have considerable problems in starting due to the fact that the rotor must pass from a condition in which its speed is zero to a condition in which it is frequency-locked with the power supply source.
If the power supply source is the ordinary power distribution grid, the frequency is 50 or 60 Hz, and in these conditions the rotor would have to attain synchronous speed in a time equal to one half-period.
This is very often troublesome, especially when the rotor has a significant mass and when the starting contrast torque is nonzero.
In practice, one may say that the problem always occurs in all motors of this type.
Many solutions have been sought in order to overcome this problem and to allow use of this type of motor, which is advantageous as regards efficiency and speed stability once the power supply grid frequency is locked onto.
However, known solutions are particularly complicated and consequently expensive, and are therefore such that they cannot be used conveniently in motors which must have a low cost.
These solutions entail, by means of memories residing within the electronic device, the application of a current having an effect equivalent to that of a current having a frequency which varies from zero to the running value in a preset time.
In practice, the rotor, independently of its actual conditions, is accelerated by means of a transient until it can then be locked directly onto the mains power supply.
As mentioned, the componentry of these devices is complicated and expensive.